A homeless man sleeps under an American flag blanket on a park bench in Brooklyn on Sept. 10, 2013. Photo Credit: Getty Images

It's Independence Day weekend, which means that it is time for barbecues, illegal fireworks and gratuitous displays of nationalism. This year, I'm planning to get matching bald eagle tattoos on my biceps. But for me, at least, Independence Day is also an opportunity for reflection on who we are as a nation and where we're headed. I'll admit that I'm worried.

Earlier this week, Belgium eliminated the United States from the World Cup. But consider that there is a decent chance that Belgium might not exist by the time the next World Cup rolls around, because of the bitter divide between its Flemish speakers and its French speakers. I say this with a heavy heart. Yes, Belgium. Congratulations on scoring your goals. Now enjoy the dustbin of history as your nation is torn apart by deep-seated ethnopolitical resentment.

Meanwhile, the United States, a sprawling and spectacularly diverse continental republic with a heavily armed and famously irascible population more than 28 times that of Belgium, will almost certainly be around come 2018, at which point we will easily trounce the soccer teams of Flanders, Wallonia and the Grand Duchy of Brussels, or whatever random assortment of states emerges from Belgium's wreckage.

But Belgium-bashing aside, we Americans should not rest on our laurels. America is big, awesome and beautiful. We're also divided in ways we can't afford to ignore.

This is not to say that the union is tottering on the brink of collapse. There are many good reasons as to why the United States has stayed intact for so long. We had the bloody Civil War some years ago, and the idea of secession has long been discredited as a result. Recent years have seen a number of peaceful secessions, such as the "velvet divorce" between the Czech Republic and Slovakia. It is far from obvious that the United States would be willing to use its military might to coerce Hawaii or Alaska from leaving the union if, for whatever reason, their electorates were determined to do so. So I doubt that it is the threat of chaos and violence alone that keeps us together.

Unlike Belgium, the United States does not have linguistic divisions that map relatively neatly onto geographical divisions, which helps dampen secessionist sentiment. Yet there is no question that the differences in the cultural sensibilities of, say, the Deep South and the Pacific Northwest are far greater than the differences between Ontario and America's neighboring Great Lakes states. A few wild-eyed dreamers have thus wondered if we've necessarily divvied up North America in the right way, from environmentalists dreaming of an "Ecotopia" west of the Cascade Mountains to white nationalists looking to build an Aryan ethnostate in northern Idaho and Montana. George Kennan, the renowned foreign policy thinker and all-purpose crank, fantasized late in life about a fragmentation of the United States not unlike that which befell the Soviet Union.

Could America break apart along religious lines, with devout Christians going one way and the rest of us going another? Think of the old "Jesusland" meme - the map of a North America divided between "Jesusland," the states that backed George W. Bush in the 2004 presidential election, and "the United States of Canada," consisting of the states that backed John Kerry and Canada that delighted liberals enraged by Bush's re-election.

At least some devout religious believers fear that as the ranks of the religiously unaffiliated grow, and as secular Americans insist on imposing their values on others, the faithful might face persecution. In 2000, Father John McCloskey, a conservative Catholic with a polarizing reputation, penned a controversial fictional take on how America might break apart. In it, a new religiously infused country, the Regional States of North America, secedes from the United States in the wake of a "short and relatively bloodless conflict" with their secularist oppressors.

Fortunately, good sense usually prevails. Way back in March of 2012, Vice President Joe Biden, he of the loose lips, told an audience at Iowa State University that the Obama administration had "screwed up" the first version of its contraception mandate by failing to provide some accommodation for religious nonprofits that wanted no part of it. Yet the president did eventually accommodate religious nonprofits. And though the White House didn't want to extend this accommodation to companies like Hobby Lobby, the Supreme Court intervened to suggest, gently, that if the accommodation worked for religious nonprofits - that is, if the goals of the contraception mandate could still be achieved without forcing these organizations to do something they'd prefer not to do - it could work for closely held private companies. Rough-and-ready compromises like this one are why McCloskey's nightmare vision will never come close to coming to pass.

But there are other threats to American national unity looming on the horizon. My admittedly unscientific sense is that we are living through a period in which Americans' sense of solidarity or group cohesiveness is declining. Liberals tend to see this decline in solidarity as a symptom of income and wealth inequality. Conservatives blame it on a rising emphasis on ethnic identity over national identity, or the turn to moral relativism. I see it as a product of the economic and social isolation of huge chunks of our population.

One challenge is a thoughtless immigration policy, which makes it hard for immigrants currently living and working in the United States to find a foothold in American life. When we debate immigration policy, we tend to focus on the economic impact of future immigration on native-born workers. What we forget is that 13 percent of the people living in the United States were born abroad, and immigrants make up 16.3 percent of the U.S. workforce.

These immigrants are already a part of our society, and their interests should count for something. While some of these immigrants are the kind of high-fliers who found Silicon Valley startups and hedge funds, far more of them are people with modest skills who are struggling to find their footing in a changing economy. Poverty among naturalized immigrants - that is, those who have become U.S. citizens - is lower than poverty among native-born Americans. Poverty among unauthorized immigrants, however, is extremely, heartbreakingly high, both because it is hard to make a living when you're living in the shadows, but also because unauthorized immigrants tend to have the lowest skill levels.

If we grant legal status to unauthorized immigrants, and if we accept that we have a responsibility to protect the interests of the immigrants who currently live and work in the United States, the last thing we should do is increase future immigration, which will intensify labor market competition for these workers. Moreover, it will tend to delay the assimilation process, as immigrants will be less likely to settle in integrated neighborhoods and form bonds with Americans from backgrounds different from their own.

Then there is the intense concentration of poverty, the issue that keeps me up at night. While 14.9 percent of the U.S. population was below the poverty line in 2010, a quarter of all poor Americans lived in neighborhoods with poverty rates above 20 percent. These "poverty areas" are, as a general rule, disconnected from employment opportunities and high-quality educational options, and their inhabitants suffer from disproportionately high rates of violent crime and incarceration.

The result is that the legitimacy of American institutions - the criminal justice system in particular, but other institutions as well - is on shaky ground in these parts of the country, as they seem to be rigged against those who live in them. There is no danger that America's poor neighborhoods will secede from the United States. The real problem is that the rest of us have, in a cultural and spiritual sense, seceded from these neighborhoods.